Source study of three moderate size recent earthquakes in the Guerrero seismic gap

Abstract

We study three recent earthquakes of different types in the Guerrero seismic gap zone with M ≥ 6.5: the 15 July 1996 Guerrero near-coast interplate earthquake (Mw = 6.6), the 18 April 2002 Guerrero near-trench interplate earthquake (Mw = 6.7), and the 11 December 2011 Guerrero normal-faulting inslab earthquake (Mw = 6.5). We compute the slip distributions, estimate source parameters, and model strong ground motions with the finite-fault stochastic method. We use different methods to estimate source parameters in order to observe differences in stress drop and radiated seismic energy among these events. The similarity in seismic magnitude gives us the opportunity to compare our results for the three different types of earthquake and interpret them in terms of the tectonic environments and seismic hazard. We analyze the peak ground accelerations and their relation with the stress drop. We simulated ground motions with the stochastic method. The model parameters are validated against recordings and a stress drop of 3, 15, and 70 MPa is estimated for the near-trench interplate, near-coast interplate, and normal-faulting inslab events, respectively. The near-trench interplate event has the lowest radiated seismic energy and the lowest rupture velocity. This is reflected in the energy to moment ratio of 2.17 × 10−6, 4.52 × 10−6, and 3.96 × 10−6 for the near-trench interplate, near-coast interplate, and normal-faulting inslab events, respectively. We define asperities using two different criteria: (1) based on average displacement and (2) maximum displacement. The asperity area for the near-coast and near-trench interplate events represents about 23 and 24–25 % of the total rupture area, which in the case of the normal-faulting inslab event, it is only 19 and 23 % based on average and maximum displacement, respectively.